This invention relates to an improved bodymaker punch and ram and more particularly to the particular structural limitations of the ram and punch which provide increased durability and thus enhanced life.
In the art of making two-piece cans, a typical method of manufacture consists of making a circular blank and then drawing the blank to form a shallow cup. The shallow cup is then redrawn to reduce its diameter and deepen the cup. The resulting cup is then wall-ironed to reduce the wall thickness and further deepen the cup to ultimately provide the body for a two-piece can. To produce the body of a two-piece can the cup is entered by a punch element and is forced thereby through a wall-ironing tool pack which may consist of one or more ironing rings. In this operation the wall thickness is reduced to the required final dimension, and the wall length is increased to somewhat more than the required final length. A bottom forming or doming operation is then performed on the integral end and finally the free end of the formed can body is trimmed to the required length.
The presses for directing the movement of the punch may be either mechanical or hydraulic. Exemplary of such machines are U.S. Pat. Nos. 3,702,559 to Hassellbeck et al. entitled "Can Bodymaking Machine" and 3,855,862 to Moller entitled "Draw and Wall Iron Process for Metal Cans".
Punches for use in manufacturing steel cans are made of tungsten carbide since tungsten carbide has been found to be inert and resist adherence to the steel. This increases the ease with which a can body may be stripped from the bodymaker punch. While the use of a tungsten carbide punch increases the ease of stripping the can body from the punch, other desirable characteristics are decreased. The punch is inherently weaker when compared with a steel punch because of the inherent characteristics of the tungsten carbide which is very brittle and very expensive.
A punch is traditionally joined to a ram for reciprocal movement relative to a die box wherein a preformed cup is modified into a can body. The rapid movement of the punch and the extreme stresses exerted thereon during its cycle result in a short punch life. The nose area of the punch is particularly vulnerable to stresses and is the primary area of punch failure. As the ram reciprocates in and out of the die box, it is also subject to varying stresses which sometime results in the ram being kinked or slightly bent at the point where the rearmost area of the punch engages the ram.
The punch is joined to the ram by a punch mounting nut which is threadably located within the ram. This results in asymetrical loading of the punch. The flange of the nut does not evenly engage the flange and thus results in varying pressure being exerted on the punch about its periphery. Consequently, there is an increased likelihood that the punch will fracture. This problem is more critical when a tungsten carbide punch is being used than when a steel punch is being used.